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I have a dual-boot system with Trisquel GNU/Linux and Windows 8.1, using the GRUB bootloader. However, I am having a problem where, every time I boot into Windows, it seems to be overwriting GRUB, so that on subsequent boots, it boots straight into Windows. I know how to boot into a live USB and re-install GRUB, but it is becoming a real pain to have to do it every time I boot into Windows. I need a longer-term solution to prevent Windows from overwriting my bootloader.

I am aware of this existing question at Unix & Linux SE:

https://unix.stackexchange.com/questions/68581/how-can-i-prevent-windows-from-overwriting-grub-when-using-a-dual-boot-machine

However, the answers there have not helped me (and may be out of date). I have disabled Windows automatic updates and I have verified that no Windows update has been performed since last year. (I posted a follow-up on U&L SE and they recommended I try here instead).

So, does anyone know how I can absolutely prevent Windows from ever overwriting my bootloader, without my permission?

Please note that I am not looking for advice on how to re-install GRUB. I know how to do that and have done it countless times. I need a more sustainable solution to prevent Windows from screwing with my boot sector in the first place.

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  • UEFI or Legacy? – user772515 Feb 27 '18 at 1:19
  • @MichaelBay UEFI. I have legacy boot disabled in the BIOS. – Time4Tea Feb 27 '18 at 4:10
  • If so neither Windows is overwriting Grub nor it needs to be reinstalled. There are two reason for your reported issue: 1. Windows somehow is putting itself as first boot priority (happens in some cases with feature updates) which is rare (never happened to me) or 2. You have a "broken UEFI" that violates UEFI standards and tends to boot Windows only. – user772515 Feb 27 '18 at 4:20
  • Although there's really no solution for #2 except an update from the manufacturer, for #1 it's simply a matter of opening UEFI settings and select Grub (Trisquel in this case) again as the first boot priority. Then boot Trisquel and update Grub: sudo update-grub (probably, I don't know Trisquel, the command is for any Debian or derivative). – user772515 Feb 27 '18 at 4:24
  • PS - The linked guide obviously isn't applicable for your case. It's for legacy (BIOS) install and MBR only! – user772515 Feb 27 '18 at 4:25
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Following the advice of MichaelBay in the comments, I believe I have figured out what the problem was. It seems that on booting, Windows was changing the UEFI boot settings to set the Windows Boot Manager to be the default bootloader. I have to admit that I was somewhat ignorant of how UEFI booting works, but I found this page to be very helpful:

https://www.happyassassin.net/2014/01/25/uefi-boot-how-does-that-actually-work-then/

The issue was essentially the same as this question:

Windows 8 changes boot order

My machine is a Dell Inspiron 660 desktop and it seems that, unfortunately, the UEFI firmware UI for it is basically garbage. However, I was able to use the following commands at the Windows command prompt to change the bootloader back to GRUB:

bcdedit /set {bootmgr} path \EFI\trisquel\grubx64.efi
bcdedit /set {bootmgr} description GRUB

Since I did this, Windows no longer seems to be trying to change the settings and GRUB is loading up every time. Problem solved!

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